1. Field of the Invention
The present invention relates to a controller for rotating electrical machines, typically to a highly accurate flux detection technology.
2. Description of Related Art
In rotating electrical machines including a permanent magnet in the magnetic field system, the permanent magnet flux changes due to temperature rise. Moreover, when irreversible demagnetization is caused due to overheating, torque fluctuates and thus a desired output can not be obtained. For this reason, in rotating electrical machines having a permanent magnet in the magnetic field system, it is necessary to detect an interlinkage magnetic flux in the armature. As background arts for detecting an interlinkage magnetic flux in an armature, there are techniques of flux estimation or flux measurement known in the related arts, which are disclosed in, for instance, patent reference literatures 1 and 2.
Patent reference literatures 1 and 2 disclose two types of techniques. One of them includes a flux table for temperature of a permanent magnet or an armature winding, to use detected temperature of the permanent magnet or the armature winding as a reference parameter so as to obtain a magnetic flux from the flux table. The other includes a motor model or a flux estimator, to use measured value or command value of voltage, current, and rotation speed of rotating electrical machines as an input parameter so as to obtain a magnetic flux from the motor model or the flux estimator.
Patent Reference Literature 1: Japanese Laid-Open Patent Publication No. H9-51700, Patent Reference Literature 2: Japanese Laid-Open Patent Publication No. 2002-95300.
As in the former, the method using a flux table for temperature assumes a one-to-one relationship between the temperature and the magnetic flux. However, magnetic flux of a permanent magnet changes not only due to the temperature but also due to reversed magnetic field over the permanent magnet, i.e., current flowing through the armature winding. Therefore, it is necessary to sufficiently consider a change of magnetic flux of the permanent magnet due to current, so as to accurately obtain interlinkage magnetic flux in the armature.
As in the latter, in the method using a motor model or a flux estimator, it is necessary to subtract voltage drop in the armature winding from the terminal voltage of rotating electrical machines, so as to calculate the magnetic flux. However, voltage drop in the armature winding changes relative to the magnitude of the resistance of the armature winding. In addition, the magnitude of the resistance of the armature winding changes relative to the temperature change. Therefore, it is necessary to sufficiently consider the relationship between them so as to accurately obtain interlinkage magnetic flux in the armature.